The cooldown starts after the proc is consumed (after the triggering basic attack) not after the ability is cast.

Trivia

Trinity Force features the most champion statistics on one item.

Spellblade's highest possible damage is 459, making for 713.5 physical damage from the attack. This can be achieved by Illaoi, who has 153 base attack damage at level 18, with Trinity Force and Sterak's Gage.

The lowest base movement speed in the game is 325. At this speed, Trinity Force grants +16.25 movement speed.

The swords in Trinity Force's icon resemble Sheen with the two swords of Zeal (which used to be part of its build path).

The name and icon of Trinity Force are inspired by The Legend of Zelda'sTriforce.